Island



(No Model.)

' 2 Sheets-Sheet 1. M. G. PAR-MER. ELECTRICAL MBASURINGAPPARATUS.

Patented Dec. 30, .1884.

(No Model.) 2 Sheet sSh eet 2 M. G. PARMER.

ELECTRICAL MEASURING APPARATUS.

Patented Dec. 30, 1884.

. j r mmmmmmmm flag T Inca/dork .UNITED STATES PATENT" GFFI E.

MOSES e. FARMER, or unwronunnonn ISLAND.

ELECTRICAL MEASURING APPARATUS. v

SPECIFICATION forming part of Letters Patent No. 3( )9,9 37, da te d December 30, 1884.

Application filed April 29, 1884. (No model.)

f0 all whom it may concern.

Be it known that I, Moses G. FARMER, a citizen of the United States, and a resident of Newport, in the county of Newport and State of Ilthode Island, have invented certain new and useful Improvements in Electrical lileasuring Apparatus, of which the following isa specification, reference being had to the drawings accompanying and forming a part of the same.

My present invention consists in an apparatus for conveniently and readily ascertaining the internal resistance of a galvanic battery. This apparatus is designed to be used in accordance with-a method of measuring and determining the resistance of a battery, the principles of which are as follows:

It is well known that if a galvanoineter, a rlieostat, and a galvanic battery be included in a simple circuit, a given deflection of the galvanometer-needle is produced, which increases as coils or sections of the rheostat are cut out. It is also well known that if a shunt or branch circuit containing a resistance be formed across the poles the deflection of the galvanometer is reduced in proportion to the amount of the shunt-resistance. Inasmuch as these effects upon the position of the galranometer-needle are opposite in kind, it is very evident that the line-resistance may be 'wholly withdrawn and a shunt simultaneously closed without affecting the position ofthe needle if the proper relations of lineand shunt resistance exist.

From the conditions here obtaining itcan 1 be readily shown thatB :1 s, in which E is the internal resistance of the battery; R, the resistance in circuit with. the galvanome ter, which, for convenience, is herein designated as the line-resistance; G, the resistance of the galvanometer, and S that of the shunt. If we make R equal to G, we have B equal to S, or, in other words, when the line-resistshould'be simultaneous, or practically so. I

have devised an apparatus by which this may be readily done, and by means of which the other necessary steps in the process may be easily performed.

For a descriptionof the apparatus, I will now refer to the accompanying drawings.

Figure 1 is a diagram showing the different parts connected in their proper operative relations. Fig. 2 is a plan view of 'a modified form of theinstruinent, and' Fig. 3 a diagram of the circuits, illustrating the method of us ing the instrument Iuse a box or case, A, (shown in" plan in Figs. 1 and 2,) containing a given number of resistance-coils connected with the plates T of an ordinary plug or pin rheostat. The number of coils and plates varies according to the requirements of particular cases, and the connections made to obtain any number of ohms and fractions of an ohm that may be necessary. I prefer a circular disposition of the plates similar to that shown. On the box A I also place the plates 0, of a resistance of more limited capacity, the coils of which are contained in the box that incloses the others.

In the space inclo'scd by the plates T is mounted a key, D, pivoted at d, and provided with front and back stops, a b. (Shown in Fig. 3.) On each side of the key is secured a spring contactstrip, E F, over which are .stops II, with adjusting-screws Jr passing through them. The ends of strips E F are brought under the forward end of the key-'le- Yer, where is a contact-plate, e, that depresses both springs simultaneously when the key is depressed. The plate A has four bindingposts, at n o p. Post in connects with the outer row of the plates T; post a with the metal base of the key I). Connection is also made by a wire. from the base of key D to the first of the series of plates 0. By other wires connect-ion is established between the last of the series of plates (3 to the strip F, and from this to post p. The strip E is connected with the end plate of the inner row of plates T..

Fig. 2 is a form ofthe apparatus similar in all respects to that described, but provided tery, B, are connected, respectively, to the posts m n, and a galvanometer, G, connected to the posts 0 1). Post 0 is then connected to post m. The problem being to measure the internal resistance of the battery B, the resistance of the galvanometcr G and that of the resistance R are first made equal, and then the pins between plates T are shifted until a depression of the key D is followed by no movement of the galvanometer-needlc. The resistance indicated by the positions of the pins in platesT will therefore be the resistance of the battery.

It will be observed by reference to Fig. 3

that normallythe battery-circuit is through.

the resistance R and the galvanometer G. By depressing the key D, however, a path is provided around the resistance Rand at the same time the shunt-resistance S is brought into a closed circuit from the battery.

Theinstrumcnt forms a convenient and practicable device for measuring battery-resistances, the juxtaposition and arrangement of the co-operatingparts adapting it to use at all times without the necessity of making the numerous connections and tests heretofore required.

\Vhat I claim as my invention is 1. In an electrical testing or measuring apparatus, the combination, with two resistances or rheostats included in branch circuits, of

electrical connections, terminals and contacts, and a key adapted to simultaneously cut out one resistance and throw in the other, as and I for the purpose describetk 2. In an electrical testing or measuring apparatus of the kind described, the combination, with the resistances R and S, of the key having contact-points a, b, and e, the springcontacts E F adapted to be simultaneously depressed by the key and circuit connections, substantially as set forth.

3. The combination, with two resistances or rheostats, a battery, and a galvanometer, the galvanometer and one rheostat being in circuit with the battery, and the other resistance in a normally-open branch or shunt circuit thereto, of circuit connections and contacts, and a key for; cutting out the resistance of the galvauometer-circuit and closing the shunteircuit simultaneously, as and for the purpose specified.

4. The combinatiomwith the plate A, of the resistance or rheostat plates T O, the key D. contacts EF,and circuit-connectionsarranged in substantially the manner herein described.

In testimony whereof I have hereunto set my hand. this 24th day of April, 1884.

MOSES G. FARMER.

Witnesses:

AUGUSTUS S'ALZMAN, WILLIAM HEATHERTON. 

